The combination of a motor with a positive displacement pump makes it possible, particularly in twin engined aircraft, to make do with only one hydraulic pump per engine for generating said hydraulic power, said generator means generally being driven by each engine or jet of the aircraft. In such a case, it is essential that one of the engines breaking down should not prevent the undercarriage from being retracted, for instance. Undercarriages are controlled by pressurised fluid which, ultimately, represents a source of power that enables the undercarriage to be retracted, eg. by means of jacks.
To avoid such a handicap, aircraft manufacturers provide their products with a special system constituted by a hydraulic power transfer set.
Thus, the hydraulic power generated by the working pump is applied to a single transfer set motor wihich drives the pump that is coupled thereto.
Said pump is connected in the fluid circuit for providing the flow necessary for retracting the undercarriage and, of course, for all the other servo controls to be found in such aircraft.
Further, this arrangement of a hydraulic power transfer set is advantageous in that it saves equipment mass by simplifying the accessory connection means, in particular by avoiding the need for a special power take off for a spare pump and also it requires only one pump instead of two half rated pumps.
This is thus a clear advantage for having such a power transducer.
Generally speaking, power sets are already known. They are built on the basis of a pair of positive displacement pumps having barrel piston chambers or barrels of cylinders, each barrel being rotated about an axis, and with the axes being coupled to each other, usually via gear means.
Clearly such a structure operates correctly. However, it still suffers from drawbacks due to the fact that its structure is not compact, and its mass still makes an important contribution to the total aircraft load.
Preferred embodiments of the present invention provide improved hydraulic power transfer sets of compact and hence lighter structure and which are also easier to manufacture.